WI-16 Mirror Lake State Park is a 2,179-acre Wisconsin state park. The process of establishing the park began in 1962 and the park officially opened on August 19, 1966. It contains Mirror Lake, a narrow reservoir with steep sandstone sides up to 50 feet tall. The lake has a surface area of 137 acres and an average depth of 10 to 14 feet. Recessed out of the wind, the water of Mirror Lake is usually calm and often as glassy-smooth as a mirror, hence the name.